Melanie Griffith -- REUNITES WITH EX-HUBBY ... First Public Outing In 20 Years

Melanie Griffith brought a very interesting date to the premiere of her movie "Dark Tourist" this week -- her ex-husband Steven Bauer ... a guy she's BARELY been seen in public with since they divorced more than 20 years ago, TMZ has learned.

Griffith and Bauer (who famously starred in "Scarface" back in 1983) were all over each other on the red carpet ... which raised eyebrows considering Melanie's current husband, Antonio Banderas, was no where to be found.

According to our crack research team, the last time M & S were photographed on a red carpet together was back 1985 ... back when Ronald Reagan was President.

There have been rumors that Melanie and Antonio have been going through a rough patch ... which makes her decision to walk her ex down the red carpet even more curious.

Sources close to the couple tell TMZ ... despite divorcing in 1987, Melanie and Steven have remained close over the years and have worked together to co-parent their son Alexander Bauer, who also attended the premiere.

We reached out to Melanie's people -- but didn't hear anything back.